A loud speaker of, for example, the dynamic cone type is an electromechanical acoustic system which is largely composed of a field magnet, a yoke or field magnet support, a pole-piece plate, a cone or vibrator element, a cone housing, a voice coil unit, an edge or annulus member, a baffle gasket and a damper or spider as is well known in the art. The field magnet, field magnet support and pole-piece plate constitute a magnetic circuit structure of the loud speaker, while the vibrator cone, cone housing, voice coil unit, edge member, baffle gasket and spider constitute an electromagnetic acoustic structure of the speaker. The field magnet support or yoke member is attached to the field magnet and has a pole-piece portion forming an annular air gap surrounded by the pole-piece plate attached to the field magnet. The voice coil unit, connected to the vibrator cone, axially projects into this annular air gap. These component members of the loud speaker are all bonded together with use of adhesives.
Rubber-based adhesive compounds are ordinarily used for the assemblage of these component members and elements for their relatively low prices and their relatively broad adaptability to materials. Problems are however encountered in using such adhesive compounds. One of these problems results from the use of a solvent which is contained in such a prior-art adhesive compound in a relatively high concentration. The solvent contained in or used with the adhesive compound tends to form a source for environmental contamination and, in addition, requires a disproportionately large amount of time for the evaporation of the solvent until the adhesive compound is completely set between the surfaces to be coupled together. The large amount of time consumed for the evaporation of the solvent results in low production efficiency of loud speakers. Where, furthermore, loud speakers are to be inspected upon completion of the assemblage by bonding, it is important that the inspection be performed after the adhesives used are sufficiently set. If the completed assembly of a speaker is put into operation for inspection purposes before the component members bonded together with adhesives are sufficiently set, not only the dimensions and performance characteristics of the speaker as determined by the inspection would not be reliable but the members once bonded together might be displaced with respect to each other and might cause crucial degradation of the performance quality of the speaker.
In the meantime, a rubber-based adhesive usually consists of 60 to 80 percent by weight of solvent and 20 to 40 percent by weight of solid constituents as well known in the art. The solvent evaporates while the adhesive applied to the surface of a member to be bonded is being set. The coating of the adhesive on the surface of the member is thus caused to shrink during setting of the adhesive. If the solvent in the adhesive fails to be evaporated uniformly on the surface of the member and/or the solid constituents have failed to mix with the solvent sufficiently, the coating of the adhesive set on the surface will have uneven thickness distribution over the surface. If such uneven thickness distribution of an adhesive takes place between the edge member and baffle gasket or between the edge member and the cone housing of a loud speaker, the speaker would produce buzzing sounds and/or the vibrator cone cantilevered by the edge member might be caused to dislodge from its proper concentric position with respect to the edge member and the voice coil unit.
With a view to avoiding these inconveniences resulting from the use of a rubber-based adhesive compound, it has been proposed to use an adhesive compound of the rapid setting type such as an acrylic adhesive compound for the bonding of the members to constitute a loud speaker. Problems have however been still encountered by the use of such an adhesive compound for the assemblage of a loud speaker. These problems include the lack of adaptability of an acrylic adhesive compound to oil-stained surfaces of metallic components such as the field magnet and the magnet support of a loud speaker. Another problem is the selectivity of an acrylic adhesive compound to the natures of the materials to be bonded. Where the cone housing, edge member and baffle gasket of a loud speaker are constructed of different materials, adhesive compounds of different chemical compositions must be used selectively one for the bonding of the cone housing and the edge member and one for the bonding of the edge member and the baffle gasket. Where, furthermore, the edge members of different materials are used depending upon the configurations and/or the materials of the vibrator cones of loud speakers of different types, adhesive compounds of different chemical compositions must also be used selectively for the bonding of the edge members and vibrator cones to the associated members and elements. In these two cases, it is thus required to use different adhesive compounds depending upon the combinations and locations of the members to be bonded together. The selective use of several kinds of adhesive compounds for the assemblage of a loud speaker not only results in increases in the time, labor and cost of production but requires strict control for the selection of the adhesives during assemblage of the loud speaker. Another objectionable property of an acrylic adhesive compound is its lack of affinity to air. By reason of this property, an acrylic adhesive compound tends to fail to set on an air-permeable material such as paper and for this reason can not be used for the bonding of a baffle gasket of paper.
A prime object of the present invention is to provide a novel acrylic adhesive compound eliminating all of the above described drawbacks of known acrylic adhesives.